Digital based electronic media formats are finally on the cusp of largely replacing all of the older analog electronic media formats. In the audio media arena, digital compact discs (CDs) replaced analog vinyl records long ago. Analog magnetic cassette tapes are becoming increasingly rare and will eventually share the same fate of 8-track tapes. Second and third generation digital audio systems such as digital Mini-discs and MP3 (MPEG Audio-layer 3) files are now taking market share away from the first generation digital audio format of compact discs.
The video media has been slower to move from analog storage and transmission formats to digital storage and transmission formats than audio. The reason for this slower analog to digital transition is largely due to the massive amounts of digital information required to accurately represent video images in digital form. The massive amounts of information require very high-capacity digital storage systems with high bit-rate outputs and high-bandwidth transmission systems. Furthermore, cost of switching from analog video equipment to digital video equipment is significantly higher than the cost of switching from analog audio equipment to digital audio equipment.
However, video is now finally rapidly moving from analog storage (VHS and Beta) and analog transmission formats (NTSC and PAL) to digital storage (MPEG) and digital transmission formats (ATSC). The DVD (Digital Versatile Disc), a digital video system, has been one of the fastest selling consumer electronic products in years. DVDs have been rapidly supplanting VHS and Beta Video-Cassette Recorders (VCRs) as the pre-recorded video playback system of choice due their high video quality, very high audio quality, convenience, and extra features. A new generation of intelligent Personal Video Records (PVRs) such as TiVo and Replay have emerged that take advantage of digital video technology. The antiquated analog NTSC (National Television Standards Committee) video transmission system is now being replaced with the digital ATSC (Advanced Television Standards Committee) video transmission system that provides for 5.1 channels of CD-quality digital audio and beautiful high-definition television (HDTV) images.
Computer systems have been using various different digital video storage and transmission formats for a number of years. Among the best digital video compression and encoding systems used by computer systems have been the series of digital video encoding systems backed by the Motion Pictures Expert Group, better known as MPEG. The three most well known and widely used digital video encoding systems from MPEG are known simply as MPEG-1, MPEG-2, and MPEG-4. The MPEG-1 format was used by VideoCDs. The MPEG-2 digital video compression and encoding system is used by DVDs and the ATSC digital television system.
The MPEG-2 and MPEG-4 standards compress a series of video frames (or fields) and encode the compressed frames (or fields) into a digital stream. The video frames may be compressed as Intra-frames or Inter-frames. An Intra-frame independently defines a complete video frame without any reference to any other information. An Inter-frame defines a video frame with reference to other video frames such as previous video frames or video frames subsequent to the current video frame.
When compressing video frames, an MPEG-2 and MPEG-4 encoder usually implements a ‘rate controller’ that is used to allocate a ‘bit budget’ for each video frame that will be compressed and encoded. Specifically, the bit budget specifies the number of bits that have been allocated to encode the video frame. By efficiently allocating a bit budget to each video frame, the rate controller attempts to generate the highest quality compressed video stream without overflowing buffers (sending more video frame information than can be stored in the target device's buffers) or underflowing buffers (not sending frames fast enough such that the decoder runs out of video frames to display). Thus, to efficiently compress and encode a digital video stream, a digital video encoder should have a rate controller that makes very wise decisions on how to allocate the available bandwidth. The present invention introduces several different methods and systems for implementing a rate controller for a digital video encoder.